Heat the oven to 190˚C/170˚C fan/gas mark 5. Peel 16 floury potatoes and cut in half; if very large, cut into quarters, or leave whole if they are small. Add to a large saucepan, cover with cold water and bring to the boil for two minutes.
Drain the potatoes well, then return to the pan and cover with a lid. Add two tablespoons of flour and shake the pan to fluff up the surfaces.
Heat a roasting tray with 140g of goose fat and three tablespoons of vegetable oil, or just 150ml of olive oil, over a medium-high heat. When sizzling, carefully add the potatoes and cook, turning to brown on all sides, for five minutes.
Roast in the oven for one hour, turning every 20 minutes until crisp on the outside and floury on the inside.